Transcript No Slide Title

What prospects for Supersymmetry
at the Large Hadron Collider ?
A brief introduction to the techniques
with which ATLAS and CMS intend
to constrain Supersymmetry
Christopher.Lester @ cern.ch
LHC & Supersymmetry
What can the LHC provide if SUSY exists?
DISCOVERY ? ………………………………. YES!
• Excellent prospects
• Might even be “easy” !
• Largely model-independent
PRECISE MEASUREMENTS ? …….... Plenty!
• but more likely to be model-dependent
July 2001
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What do we want to know?
Other models:
M.S.S.M.
Squark masses (12)
The gluino mass
(1)
 Slepton masses
(9)
 Neutralino masses
(4)
 Chargino masses
 Mixing matrices
 Phases
(2)
(?)
(?)
 …..
(plenty)
 RP-Violating M.S.S.M.
 RPV couplings
(45)
 mSUGRA model
 m0, m1/2, A0, tan β, sgn μ
(5)
 A.M.S.B. model
 m0, m3/2, tan β, sgn μ
(4)
 G.M.S.B. model
 λ, Mmes, N5, tan β, sgn μ, Cgrav
(6)
There is no shortage of
parameters which need to be
determined!
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Which can we measure?
“Lots, but it depends…”
The kinds of measurements which can be
made, very much depend on the SUSY model
which nature has chosen!
It is important to understand the physical
effects of R-Parity conservation (or nonconservation) in SUSY models, before
discussing measurements.
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R-Parity: Conservation/Violation
R  (1)
3( B  L )  2 s
 R=+1 for Standard Model particles
 R= -1 for SUSY particles
Two main SUSY scenarios:
RP-Conserving
RP-Violating
(RPV/RPC)
(L.S.P. = “lightest SUSY particle”)
How stable is the
lightest SUSY
particle (L.S.P.) ?
RPC Stable
Large
missing
energy?
Yes
Event can be Sparticle
reconstructed production
fully?
Usually not
Only in pairs
RPV Unstable
No
Yes
(decays to leptons or jets)
July 2001
Either singly,
or in pairs
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R-Parity Conservation
RPC
L.S.P. = lightest SUSY particle
L.S.P. stable and weakly interacting,
and so “goes missing”
• Missing energy signature
• Usually incomplete event reconstruction
• Need to rely on long decay chains and
kinematic variables (endpoints and
distributions)
Sparticles are only produced in pairs
• double the trouble!
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Squark/gluon mass scale
M eff  E
missing
T
 | p
jeti
T
RPC
|
i
events
Peak of Meff distribution
correlates well with
squark/gluon mass
scale for mSUGRA and
GMSB models.
Signal
S.M.
Background
M eff (GeV)
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SUGRA Reach (CMS)
RPC
Kinematic edges: l+l- edge
RPC
 The l+l- invariant mass from the
decay chain (right) has a
kinematic endpoint.
 For 100 fb-1, edge measured at
109.10±0.13(stat) GeV
 Dominant systematic error on
lepton energy scale also ~0.1%
 In progress:
•
•
•
•
July 2001
incorporation of widths,
decay matrix elements,
polarisations,
photon radiation, etc
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Coverage of l+l- edge
However ...
RPC
… different processes can produce the
same final state.
 Can the process be identified?
• Detailed study of the shape of the
mll distribution can provide clues
 Likely coverage?
• Lepton edge observable over
significant region of m0, m1/2
parameter space (CMS plot left)
 Likely outcome?
 Precise sparticle mass differences
 When chains are long enough, resolution on
absolute mass scale improves and can
measure mass of L.S.P.
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R-Parity Violation
RP-Violating:
RPV
L.S.P. = lightest SUSY particle
L.S.P. decays into leptons or jets:
• If L.S.P. lifetime is short:
 Multi-jet or multi-lepton signature
 No missing energy, so reconstruct full event
• If L.S.P. lifetime is long: looks like RPC scenario
Sparticles may be produced singly
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Lepton number violating RPV
 λ’ijk couples a slepton to two quarks
 Can have resonant sneutrino production
 Cross section can place lower bound on λ’ijk
 Expect to observe (within 3 years) either
Reconstructed neutralino
mass peak in mjjμ invariant
mass distribution
 900 GeV neutrino if λ’211>0.05
 350 GeV neutrino if λ’211>0.01
 (present limit: ' 211  0.06 ( M d~ / 100 GeV) )
R
λ’ijk =0.09
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Baryon number violating RPV
 Each L.S.P. decays to three quarks
(u,d,s) forming three jets (jjj)
 Require 2 leptons and at least 8 jets:
(j+jjj)+(j+ll+jjj)
 Look for L.S.P. / chargino peak in
mjjj / m jjjll plane msquark L = 638 ± 5 ±12 GeV
mneutralino 2
0.3
± 4 GeV
= 212 ±
mslepton R = 155 ± 3 ± 3 GeV
July 2001
mneutralino 1
= 117 ±
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the LHC : [email protected]
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Conclusions
 We can expect ATLAS and CMS to
 Observe squarks and gluons
below 2.5 TeV and
observe sleptons below 300 GeV
in inclusive measurements.
 Accurately measure squark, slepton
and neutralino masses using
cascade decays (provided chains are
sufficiently long and rates are
favourable)
Other areas of completed and ongoing research
which there was not time to discuss:







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
N.L.S.P. lifetime in G.M.S.B. models
(Non-pointing photons / slow heavy leptons)
A.M.S.B. models
Lepton flavour violation (via slepton mixing)
Measuring the gaugino mixing matrix
Direct slepton production
Non-minimal models
SUSY Higgs sector
Everything else which I have forgotten to mention ...
 Success is expected in both RPV
and RPC scenarios
 Precise measurements:
many can
be made in principle, but which of them can
measured in practice will depend strongly
on the model which nature has chosen
July 2001
CMS
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R-Parity: conservation/violation
 R=+1 for Standard Model particles
 R= -1 for SUSY particles
R  (1)
3( B  L )  2 s
Two main SUSY scenarios:
RPV/RPC
RP-Conserving:
RP-Violating:
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R-Parity: conservation/violation
L.S.P.
RPC Stable
Large
missing
energy?
Yes
Event can be Sparticle
reconstructed production
fully?
Usually not
Only in pairs
RPV Unstable
No
Yes
(decays to leptons or jets)
Either singly,
or in pairs
L.S.P. = lightest SUSY particle
July 2001
HEP2001 : SUSY at the LHC : [email protected]
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